Voice over Internet Protocol (VoIP) is a technology allowing voice information to be transmitted within packets over a data network such as the Internet. VoIP signals may be transmitted over regular telephone lines or over “cable” lines that are configured to carry cable television signals. When a personal computer (PC) is connected to the data network via a cable system, data can be transferred at a rate many times greater than the data transfer rate of regular telephone lines. With cable services, a routing device, such as a cable modem, is typically used to allow a PC at the customer premises to access the data network. The cable modem also routes telephone signal transmissions to and from a telephone at the customer premises. Cable modems typically adhere to well-defined standards, such as the Data Over Cable Service Interface Specification (DOCSIS) developed by CableLabs. The most recent version of this standard (DOCSIS 2.0) was released in January 2002.
Regarding VoIP on a cable system, a cable modem is usually configured to give voice signals priority over data or Internet Protocol (IP) signals. In this way, voice signals can be communicated quickly without noticeable delay, even if Internet traffic is heavy. The DOCSIS configuration file stored on the cable modem includes an assignment of a bit rate allocation for different types of signals and a priority list regarding what type of signal is handled before the others. The priority, among other things, is defined according to fields referred to as “service flows”. Usually, a service flow defines the type of signals that may correspond to a particular customer device, e.g. a telephone, to establish a priority in which certain signals, e.g. telephone signals, are prioritized over other types of data signals. The configuration file typically defines upstream and downstream signals separately.
During a telephone call over a cable network, two (or more) telephones are linked through the network to allow telephone signals to be transmitted back and forth between the telephones. A dedicated communication path is temporarily established between the two telephone devices. To more efficiently communication along this dedicated communication path, one customer device can transmit a message known as an Address Resolution Protocol (ARP) message. ARP messages are transmitted out over the network to resolve the MAC address of another device on the network. An ARP message contains a known IP address and requests that the device having that IP address returns a message indicating its MAC address. By resolving the MAC address of the other device, the two devices can communicate with each other using MAC addresses if the two devices are on the same IP sub-net. PCs and other devices also send out ARP messages to resolve MAC addresses.
In DOCSIS, ARP messages can be defined within the configuration file stored in the cable modem. For example, ARP messages can be classified under a particular service flow. If ARP messages are classified under a service flow having a high priority, then all the ARP messages received by the cable modem will be given a high priority and will be sent within the high-priority channel, e.g. a voice (signaling) channel. On the other hand, if the ARP messages are classified under a service flow having a lower priority, then all the ARP messages received by the cable modem will be given a lower priority and will be sent within the low-priority channel, e.g. an IP channel.
One problem with this current system is that DOCSIS does not allow ARP messages to be further restricted. Therefore, if ARP messages are given a high priority, then all ARP messages, even those from the lower-priority IP sources, e.g. a PC, are sent within the high-priority channel. These lower-priority ARP messages can thus congest the high-priority channel. Another problem is that, if ARP messages are not given high priority, then high-priority ARP messages from high-priority sources, e.g. a telephone, are sent within the low-priority channel. These high-priority ARP messages can thus be delayed by Internet traffic. Neither of these consequences is desirable and thus a need exists in the industry to address these and other deficiencies and inadequacies.